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RFC 8796: RSVP-TE Summary Fast Reroute Extensions for Label Switched Path (LSP) Tunnels

  • M. Taillon,  
  • T. Saad, Ed.,  
  • R. Gandhi,  
  • A. Deshmukh,  
  • M. Jork,  
  • V. Beeram
Proposed Standard
RFC Tips

Abstract

This document updates RFC 4090 for the Resource Reservation Protocol (RSVP) Traffic Engineering (TE) procedures defined for facility backup protection. The updates include extensions that reduce the amount of signaling and processing that occurs during Fast Reroute (FRR); as a result, scalability when undergoing FRR convergence after a link or node failure is improved. These extensions allow the RSVP message exchange between the Point of Local Repair (PLR) and the Merge Point (MP) nodes to be independent of the number of protected Label Switched Paths (LSPs) traversing between them when facility bypass FRR protection is used. The signaling extensions are fully backwards compatible with nodes that do not support them.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8796.

1. Introduction

The Fast Reroute (FRR) procedures defined in [RFC4090] describe the mechanisms for the Point of Local Repair (PLR) to reroute traffic and signaling of a protected RSVP-TE Label Switched Path (LSP) onto the bypass tunnel in the event of a TE link or node failure. Such signaling procedures are performed individually for each affected protected LSP. This may eventually lead to control-plane scalability and latency issues on the PLR and/or the Merge Point (MP) nodes due to limited memory and CPU processing resources. This condition is exacerbated when the failure affects a large number of protected LSPs that traverse the same PLR and MP nodes.

For example, in a large-scale deployment of RSVP-TE LSPs, a single Label Switching Router (LSR) acting as a PLR node may host tens of thousands of protected RSVP-TE LSPs egressing the same protected link and also act as an MP node for a similar number of LSPs that ingress on the same link. In the event of the failure of the link or neighbor node, the RSVP-TE control plane of the node (when acting as a PLR node) becomes busy rerouting protected LSPs over the bypass tunnel(s) in one direction and (when acting as an MP node) becomes busy merging RSVP states from signaling received over bypass tunnels for one or more LSPs in the reverse direction. Subsequently, the head-end Label Edge Routers (LERs) that are notified of the local repair at any downstream LSRs will attempt to (re)converge the affected RSVP-TE LSPs onto newly computed paths -- possibly traversing the same previously affected LSR(s). As a result, the RSVP-TE control plane becomes overwhelmed (1) by the amount of FRR RSVP-TE processing overhead following the link or node failure and (2) due to other control-plane protocols (e.g., IGP) that undergo convergence on the same node at the same time.

Today, each protected RSVP-TE LSP is signaled individually over the bypass tunnel after FRR. The changes introduced in this document allow the PLR node to assign multiple protected LSPs to a bypass tunnel group and to communicate this assignment to the MP, such that upon failure, the signaling over the bypass tunnel happens on one or more bypass tunnel groups. This document defines new extensions that

  1. update the procedures defined in [RFC4090] for facility backup protection, to enable the MP node to become aware of the PLR node's bypass tunnel assignment group or groups.
  2. allow FRR procedures between the PLR and the MP nodes to be signaled and processed on one or more per-bypass tunnel groups.

As defined in [RFC2961], summary refresh procedures use MESSAGE_ID to refresh the RSVP Path and Resv states to help with scaling. The Summary FRR procedures introduced in this document build on those concepts to allow the MESSAGE_ID(s) to be exchanged on one or more per-bypass tunnel assignment groups and continue to use summary refresh procedures while reducing the amount of messaging that occurs after rerouting signaling over the bypass tunnel post-FRR.

2. Conventions Used in This Document

2.1. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2.2. Acronyms and Abbreviations

It is assumed that the reader is familiar with the terms and abbreviations used in [RFC3209] and [RFC4090].

The following abbreviations are also used in this document:

LSR:
Label Switching Router
LER:
Label Edge Router
MPLS:
Multiprotocol Label Switching
LSP:
Label Switched Path
MP:
Merge Point node as defined in [RFC4090]
PLR:
Point of Local Repair node as defined in [RFC4090]
FRR:
Fast Reroute as defined in [RFC4090]
B-SFRR-Ready:
Bypass Summary FRR Ready Extended ASSOCIATION object. Added by the PLR node for each LSP protected by the bypass tunnel
B-SFRR-Active:
Bypass Summary FRR Active Extended ASSOCIATION object. Used to notify the MP node that one or more groups of protected LSPs have been rerouted over the associated bypass tunnel
MTU:
Maximum Transmission Unit

3. Extensions for Summary FRR Signaling

The RSVP ASSOCIATION object is defined in [RFC4872] as a means to associate LSPs with each other. For example, in the context of one or more GMPLS-controlled LSPs, the ASSOCIATION object is used to associate a recovery LSP with the LSP(s) it is protecting. The Extended ASSOCIATION object is introduced in [RFC6780] to expand on the possible usage of the ASSOCIATION object and generalize the definition of the Extended Association ID field.

This document defines the use of the Extended ASSOCIATION object to carry the Summary FRR information and associate the protected LSP or LSPs with the bypass tunnel that protects them. Two new Association Types for the Extended ASSOCIATION object, and new Extended Association IDs, are defined in this document to describe the Bypass Summary FRR Ready (B-SFRR-Ready) and Bypass Summary FRR Active (B‑SFRR-Active) associations.

The PLR node creates and manages the Summary FRR LSP groups (identified by Bypass_Group_Identifiers) and shares the group identifiers with the MP via signaling.

A PLR node SHOULD assign the same Bypass_Group_Identifier to all protected LSPs provided that the protected LSPs:

  • share the same outgoing protected interface,
  • are protected by the same bypass tunnel, and
  • are assigned the same tunnel sender address that is used for backup path identification after FRR as described in [RFC4090].

This minimizes the number of bypass tunnel Summary FRR groups and optimizes the amount of signaling that occurs between the PLR and the MP nodes after FRR.

A PLR node that supports Summary FRR procedures adds an Extended ASSOCIATION object with a B-SFRR-Ready Extended Association ID in the RSVP Path message of the protected LSP. The PLR node adds the protected LSP Bypass_Group_Identifier, information from the assigned bypass tunnel, and a MESSAGE_ID object into the B-SFRR-Ready Extended Association ID. The MP uses the information contained in the received B-SFRR-Ready Extended Association ID to refresh and merge the protected LSP Path state after FRR occurs.

An MP node that supports Summary FRR procedures adds the B-SFRR-Ready Extended ASSOCIATION object and respective Extended Association ID in the RSVP Resv message of the protected LSP to acknowledge the PLR's bypass tunnel assignment and provide the MESSAGE_ID object that the MP node will use to refresh the protected LSP Resv state after FRR occurs.

The MP maintains the PLR node group assignments learned from signaling and acknowledges the group assignments to the PLR node via signaling. Once the PLR node receives the group assignment acknowledgment from the MP, the FRR signaling can proceed based on Summary FRR procedures as described in this document.

The B-SFRR-Active Extended ASSOCIATION object with Extended Association ID is sent by the PLR node after activating the Summary FRR procedures. The B-SFRR-Active Extended ASSOCIATION object with Extended Association ID is sent within the RSVP Path message of the bypass tunnel to inform the MP node that one or more groups of protected LSPs protected by the bypass tunnel are now being rerouted over the bypass tunnel.

3.1. B-SFRR-Ready Extended ASSOCIATION Object

The Extended ASSOCIATION object is populated using the rules defined below to associate a protected LSP with the bypass tunnel that is protecting it when Summary FRR procedures are enabled.

The Association Type, Association ID, and Association Source MUST be set as defined in [RFC4872] for the ASSOCIATION object. More specifically:

Association Source:
The Association Source is set to an address of the PLR node.
Association Type:
A new Association Type is defined for B-SFRR-Ready as follows:
Table 1: The B-SFRR-Ready Association Type
Value Type
5 Bypass Summary FRR Ready Association (B-SFRR-Ready)

The Extended ASSOCIATION object's Global Association Source MUST be set according to the rules defined in [RFC6780].

The B-SFRR-Ready Extended Association ID is populated by the PLR node when performing Bypass Summary FRR Ready association for a protected LSP. The rules governing its population are described in the subsequent sections.

3.1.1. IPv4 B-SFRR-Ready Extended Association ID

The IPv4 Extended Association ID for the B-SFRR-Ready Association Type is carried inside the IPv4 Extended ASSOCIATION object and has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Bypass_Tunnel_ID      |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Bypass_Source_IPv4_Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Bypass_Destination_IPv4_Address                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Bypass_Group_Identifier                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                MESSAGE_ID                                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The IPv4 Extended Association ID for B-SFRR-Ready
Bypass_Tunnel_ID:

16 bits

The bypass tunnel identifier.

Reserved:

16 bits

Reserved for future use. MUST be set to zero when sending and ignored on receipt.

Bypass_Source_IPv4_Address:

32 bits

The bypass tunnel source IPv4 address.

Bypass_Destination_IPv4_Address:

32 bits

The bypass tunnel destination IPv4 address.

Bypass_Group_Identifier:

32 bits

The bypass tunnel group identifier that is assigned to the LSP.

MESSAGE_ID:
A MESSAGE_ID object as defined by [RFC2961].

3.1.2. IPv6 B-SFRR-Ready Extended Association ID

The IPv6 Extended Association ID for the B-SFRR-Ready Association Type is carried inside the IPv6 Extended ASSOCIATION object and has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Bypass_Tunnel_ID      |           Reserved            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                Bypass_Source_IPv6_Address                     +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                Bypass_Destination_IPv6_Address                +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Bypass_Group_Identifier                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                MESSAGE_ID                                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The IPv6 Extended Association ID for B-SFRR-Ready
Bypass_Tunnel_ID:

16 bits

The bypass tunnel identifier.

Reserved:

16 bits

Reserved for future use. MUST be set to zero when sending and ignored on receipt.

Bypass_Source_IPv6_Address:

128 bits

The bypass tunnel source IPv6 address.

Bypass_Destination_IPv6_Address:

128 bits

The bypass tunnel destination IPv6 address.

Bypass_Group_Identifier:

32 bits

The bypass tunnel group identifier that is assigned to the LSP.

MESSAGE_ID:
A MESSAGE_ID object as defined by [RFC2961].

3.1.3. Processing Rules for B-SFRR-Ready Extended ASSOCIATION Object

A PLR node assigns a bypass tunnel and Bypass_Group_Identifier for each protected LSP. The same Bypass_Group_Identifier is used for the set of protected LSPs that share the same bypass tunnel, traverse the same egress link, and are not already rerouted. The PLR node MUST generate a MESSAGE_ID object with Epoch and Message_Identifier set according to [RFC2961]. The MESSAGE_ID object Flags MUST be cleared when transmitted by the PLR node and ignored when received at the MP node.

A PLR node MUST generate a new Message_Identifier each time the contents of the B-SFRR-Ready Extended Association ID change (e.g., when the PLR node changes the bypass tunnel assignment).

A PLR node notifies the MP node of the bypass tunnel assignment via adding a B-SFRR-Ready Extended ASSOCIATION object and Extended Association ID in the RSVP Path message for the protected LSP, using the procedures described in Section 3.3.

An MP node acknowledges the assignment to the PLR node by signaling the B-SFRR-Ready Extended ASSOCIATION object and Extended Association ID within the RSVP Resv message of the protected LSP. With the exception of the MESSAGE_ID object, all other fields from the received B-SFRR-Ready Extended Association ID in the RSVP Path message are copied into the B-SFRR-Ready Extended Association ID to be added in the Resv message. The MESSAGE_ID object is set according to [RFC2961]. The MESSAGE_ID object Flags MUST be cleared when transmitted by the MP node and ignored when received at the PLR node. A new Message_Identifier MUST be used to acknowledge an updated PLR node's assignment.

A PLR node considers the protected LSP as Summary FRR capable only if all the fields in the B-SFRR-Ready Extended Association ID that are sent in the RSVP Path message match the fields received in the RSVP Resv message (with the exception of the MESSAGE_ID). If the fields do not match or if the B-SFRR-Ready Extended ASSOCIATION object is absent in a subsequent refresh, the PLR node MUST consider the protected LSP as not Summary FRR capable.

A race condition may arise for a previously Summary FRR-capable protected LSP when the MP node triggers a refresh that does not contain the B-SFRR-Ready Extended ASSOCIATION object, while at the same time the PLR triggers Summary FRR procedures due to a fault occurring concurrently. In this case, it is possible that the PLR triggers Summary FRR procedures on the protected LSP before it can receive and process the refresh from the MP node. As a result, the MP will receive an Srefresh with a Message_Identifier that is not associated with any state. As per [RFC2961], this results in the MP generating an Srefresh NACK for this Message_Identifier and sending it back to the PLR. The PLR processes the Srefresh NACK, replays the full Path state associated with the Message_Identifier, and subsequently recovers from this condition.

3.2. B-SFRR-Active Extended ASSOCIATION Object

The Extended ASSOCIATION object for the B-SFRR-Active Association Type is populated by a PLR node to indicate to the MP node (the bypass tunnel destination) that one or more groups of Summary FRR‑capable protected LSPs that are being protected by the bypass tunnel are being rerouted over the bypass tunnel.

The B-SFRR-Active Extended ASSOCIATION object is carried in the RSVP Path message of the bypass tunnel and signaled downstream towards the MP (the bypass tunnel destination).

The Association Type, Association ID, and Association Source MUST be set as defined in [RFC4872] for the ASSOCIATION object. More specifically:

Association Source:
The Association Source is set to an address of the PLR node.
Association Type:
A new Association Type is defined for B-SFRR-Active as follows:
Table 2: The B-SFRR-Active Association Type
Value Type
6 Bypass Summary FRR Active Association (B-SFRR-Active)
Extended Association ID for B-SFRR-Active:
The B-SFRR-Active Extended Association ID is populated by the PLR node for the Bypass Summary FRR Active association. The rules to populate the Extended Association ID in this case are described below.

3.2.1. IPv4 B-SFRR-Active Extended Association ID

The IPv4 Extended Association ID for the B-SFRR-Active Association Type is carried inside the IPv4 Extended ASSOCIATION object and has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Num-BGIDs          |          Reserved             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Bypass_Group_Identifier                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :                               |
   //                              :                              //
   |                               :                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Bypass_Group_Identifier                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                      RSVP_HOP_Object                        //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                      TIME_VALUES                            //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       IPv4 tunnel sender address              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The IPv4 Extended Association ID for B-SFRR-Active
Num-BGIDs:

16 bits

Number of Bypass_Group_Identifier fields.

Reserved:

16 bits

Reserved for future use.

Bypass_Group_Identifier:

32 bits each

A Bypass_Group_Identifier that was previously signaled by the PLR using the Extended ASSOCIATION object in the B-SFRR-Ready Extended Association ID. One or more Bypass_Group_Identifiers MAY be included.

RSVP_HOP_Object:

Class 3, as defined by [RFC2205]

Replacement RSVP_HOP object to be applied to all LSPs associated with each of the following Bypass_Group_Identifiers. This corresponds to C-Type = 1 for IPv4 RSVP_HOP.

TIME_VALUES object:

Class 5, as defined by [RFC2205]

Replacement TIME_VALUES object to be applied to all LSPs associated with each of the preceding Bypass_Group_Identifiers after receiving the B-SFRR-Active Extended ASSOCIATION object.

IPv4 tunnel sender address:
The IPv4 address that the PLR node sets to identify one or more backup paths as described in Section 6.1.1 of [RFC4090]. This address is applicable to all groups identified by any Bypass_Group_Identifiers carried in the B-SFRR-Active Extended Association ID.

3.2.2. IPv6 B-SFRR-Active Extended Association ID

The IPv6 Extended Association ID for the B-SFRR-Active Association Type is carried inside the IPv6 Extended ASSOCIATION object and has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Num-BGIDs          |          Reserved             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Bypass_Group_Identifier                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :                               |
   //                              :                              //
   |                               :                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Bypass_Group_Identifier                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                      RSVP_HOP_Object                        //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                      TIME_VALUES                            //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       IPv6 tunnel sender address              +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The IPv6 Extended Association ID for B-SFRR-Active
Num-BGIDs:

16 bits

Number of Bypass_Group_Identifier fields.

Reserved:

16 bits

Reserved for future use.

Bypass_Group_Identifier:

32 bits each

A Bypass_Group_Identifier that was previously signaled by the PLR using the Extended ASSOCIATION object in the B-SFRR-Ready Extended Association ID. One or more Bypass_Group_Identifiers MAY be included.

RSVP_HOP_Object:

Class 3, as defined by [RFC2205]

Replacement RSVP_HOP object to be applied to all LSPs associated with each of the following Bypass_Group_Identifiers. This corresponds to C-Type = 2 for IPv6 RSVP_HOP.

TIME_VALUES object:

Class 5, as defined by [RFC2205]

Replacement TIME_VALUES object to be applied to all LSPs associated with each of the following Bypass_Group_Identifiers after receiving the B-SFRR-Active Extended ASSOCIATION object.

IPv6 tunnel sender address:
The IPv6 address that the PLR node sets to identify one or more backup paths as described in Section 6.1.1 of [RFC4090]. This address is applicable to all groups identified by any Bypass_Group_Identifiers carried in the B-SFRR-Active Extended Association ID.

3.3. Signaling Procedures prior to Failure

Before Summary FRR procedures can be used, a handshake MUST be completed between the PLR and MP nodes. This handshake is performed using the Extended ASSOCIATION object that carries the B-SFRR-Ready Extended Association ID in both the RSVP Path and Resv messages of the protected LSP.

The facility backup method introduced in [RFC4090] takes advantage of MPLS label stacking (the PLR node imposes additional MPLS labels post-FRR) to allow rerouting of protected traffic over the backup path. The backup path may have stricter MTU requirements; due to label stacking at the PLR node, the protected traffic may exceed the backup path MTU. It is assumed that the operator engineers their network to allow rerouting of protected traffic and the additional label stacking at the PLR node in order to not exceed the backup path MTU.

When using the procedures defined in this document, the PLR node MUST ensure that the bypass tunnel assignment can satisfy the protected LSP MTU requirements post-FRR. This prevents any packets from being dropped due to exceeding the MTU size of the backup path after traffic is rerouted onto the bypass tunnel post-failure. Section 2.6 of [RFC3209] describes a mechanism to determine whether a node needs to fragment or drop a packet when it exceeds the path MTU discovered using RSVP signaling on the primary LSP path. A PLR can leverage the RSVP-discovered path MTU on the backup and primary LSP paths to ensure that the MTU is not exceeded before or after rerouting the protected traffic onto the bypass tunnel.

3.3.1. PLR Signaling Procedure

The B-SFRR-Ready Extended ASSOCIATION object is added by each PLR node in the RSVP Path message of the protected LSP to record the bypass tunnel assignment. This object is updated every time the PLR node updates the bypass tunnel assignment. This results in triggering an RSVP Path change message.

Upon receiving an RSVP Resv message with a B-SFRR-Ready Extended ASSOCIATION object, the PLR node checks to see if the expected subobjects from the B-SFRR-Ready Extended Association ID are present. If present, the PLR node determines if the MP has acknowledged the current PLR node's assignment.

To be a valid acknowledgment, the received B-SFRR-Ready Extended Association ID contents within the RSVP Resv message of the protected LSP MUST match the latest B-SFRR-Ready Extended ASSOCIATION object and Association ID contents that the PLR node had sent within the RSVP Path message (with the exception of the MESSAGE_ID).

Note that when forwarding an RSVP Resv message upstream, the PLR node SHOULD remove any/all B-SFRR-Ready Extended ASSOCIATION objects whose Bypass_Source_IPv4_Address or Bypass_Source_IPv6_Address field matches any of the PLR node addresses.

3.3.2. MP Signaling Procedure

Upon receiving an RSVP Path message with a B-SFRR-Ready Extended ASSOCIATION object, an MP node processes all (there may be multiple PLR nodes for a single MP node) B-SFRR-Ready Extended ASSOCIATION objects that have the MP node address as the bypass destination address in the Extended Association ID.

The MP node first ensures the existence of the bypass tunnel and that the Bypass_Group_Identifier is not already FRR Active. That is, an LSP cannot join a group that is already FRR rerouted.

The MP node builds a mirrored Summary FRR group database per PLR node by associating the Bypass_Source_IPv4_Address or Bypass_Source_IPv6_Address that is carried in the IPv4 or IPv6 B‑SFRR-Ready Extended Association IDs, respectively.

The MESSAGE_ID is extracted and recorded for the protected LSP Path state. The MP node signals a B-SFRR-Ready Extended ASSOCIATION object and Extended Association ID in the RSVP Resv message of the protected LSP. With the exception of the MESSAGE_ID objects, all other fields of the received B-SFRR-Ready Extended ASSOCIATION object in the RSVP Path message are copied into the B-SFRR-Ready Extended ASSOCIATION object to be added in the Resv message. The MESSAGE_ID object is set according to [RFC2961] with the Flags cleared.

Note that an MP may receive more than one RSVP Path message with the B-SFRR-Ready Extended ASSOCIATION object from one or more different upstream PLR nodes. In this case, the MP node is expected to save all the received MESSAGE_IDs received from the different upstream PLR nodes. After a failure, the MP node determines and activates the state(s) associated with the Bypass_Group_Identifier(s) received in the RSVP Path message containing the B-SFRR-Active Extended ASSOCIATION object that is signaled over the bypass tunnel from the PLR node, as described in Section 3.4.

When forwarding an RSVP Path message downstream, the MP node SHOULD remove any/all B-SFRR-Ready Extended ASSOCIATION objects whose Bypass_Destination_IPv4_Address or Bypass_Destination_IPv6_Address field matches any of the MP node addresses.

3.4. Signaling Procedures Post-Failure

Upon detection of a fault (egress link or node failure), the PLR node will first perform the object modification procedures described by Section 6.4.3 of [RFC4090] for all affected protected LSPs. For the Summary FRR-capable LSPs that are assigned to the same bypass tunnel, a common RSVP_HOP and SENDER_TEMPLATE MUST be used.

The PLR node MUST signal non-Summary FRR-capable LSPs over the bypass tunnel before signaling the Summary FRR-capable LSPs. This is needed to allow for the case where the PLR node recently changed a bypass assignment and the MP has not processed the change yet.

The B-SFRR-Active Extended ASSOCIATION object is sent within the RSVP Path message of the bypass tunnel to reroute the RSVP state of Summary FRR-capable LSPs.

3.4.1. PLR Signaling Procedure

After a failure event, when using the Summary FRR path signaling procedures, an individual RSVP Path message is not signaled for each Summary FRR LSP. Instead, to reroute Summary FRR LSPs via the bypass tunnel, the PLR node adds the B-SFRR-Active Extended ASSOCIATION object in the RSVP Path message of the RSVP session of the bypass tunnel.

The RSVP_HOP_Object field in the B-SFRR-Active Extended Association ID is set to a common object that will be applied to all LSPs associated with the Bypass_Group_Identifiers that are carried in the B-SFRR-Active Extended Association ID.

The PLR node adds the Bypass_Group_Identifier(s) of any group or groups that have common group attributes, including the tunnel sender address, to the same B-SFRR-Active Extended Association ID. Note that multiple ASSOCIATION objects, each carrying a B-SFRR-Active Extended Association ID, can be carried within a single RSVP Path message of the bypass tunnel and sent towards the MP as described in [RFC6780].

Any previously received MESSAGE_IDs from the MP are activated on the PLR. As a result, the PLR starts sending Srefresh messages containing the specific Message_Identifier(s) for the states to be refreshed.

3.4.2. MP Signaling Procedure

Upon receiving an RSVP Path message with a B-SFRR-Active Extended ASSOCIATION object, the MP performs normal merge point processing for each protected LSP associated with each Bypass_Group_Identifier, as if it had received an individual RSVP Path message for that LSP.

For each Summary FRR-capable LSP that is being merged, the MP first modifies the Path state as follows:

  1. The RSVP_HOP object is copied from the RSVP_HOP_Object field in the B-SFRR-Active Extended Association ID.
  2. The TIME_VALUES object is copied from the TIME_VALUES field in the B-SFRR-Active Extended Association ID. The TIME_VALUES object contains the refresh period of the PLR node, and it is used to generate periodic refreshes. The TIME_VALUES object carried in the B-SFRR-Active Extended Association ID matches the one that would have been exchanged in a full Path message sent to the MP after the failure when no Summary FRR procedures are used.
  3. The tunnel sender address field in the SENDER_TEMPLATE object is copied from the tunnel sender address field of the B-SFRR-Active Extended Association ID.
  4. The Explicit Route Object (ERO) is modified as per Section 6.4.4 of [RFC4090]. Once the above modifications are completed, the MP node performs merge processing as per [RFC4090].
  5. Any previously received MESSAGE_IDs from the PLR node are activated. The MP is allowed to send Srefresh messages containing the specific Message_Identifier(s) for the states to be refreshed.

A failure during merge processing of any individual rerouted LSP MUST result in an RSVP PathErr message.

An individual RSVP Resv message for each successfully merged Summary FRR LSP is not signaled. The MP node SHOULD immediately use summary refresh procedures to refresh the protected LSP Resv state.

3.5. Refreshing Summary FRR Active LSPs

The refreshing of Summary FRR Active LSPs is performed using summary refresh as defined by [RFC2961].

4. Backwards Compatibility

The (Extended) ASSOCIATION object is defined in [RFC4872] with a class number in the form 11bbbbbb, where b=0 or 1. This ensures compatibility with nodes that do not provide support, in accordance with the procedures specified in Section 3.10 of [RFC2205] regarding unknown-class objects. Such nodes will ignore the object and forward it without any modification.

5. Security Considerations

This document updates an existing RSVP object -- the Extended ASSOCIATION object as described in Section 3. Thus, in the event of the interception of a signaling message, slightly more information could be deduced about the state of the network than was previously the case.

When using the procedures defined in this document, FRR signaling for rerouting of the states of one or more protected LSPs onto the bypass tunnel can be performed on a group of protected LSPs with a single RSVP message. This allows an intruder to potentially impact and manipulate a set of protected LSPs that are assigned to the same bypass tunnel group. Note that such an attack is possible even without the mechanisms defined in this document, albeit at an extra cost resulting from the excessive per-LSP signaling that will occur.

Existing mechanisms for maintaining the integrity and authenticity of RSVP messages [RFC2747] can be applied. Other considerations mentioned in [RFC4090] and [RFC5920] also apply.

6. IANA Considerations

IANA maintains the "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Parameters" registry. The "Association Type" subregistry is included in this registry.

This registry has been updated with the new Association Types for the Extended ASSOCIATION objects defined in this document as follows:

Table 3: New Extended ASSOCIATION Object Association Types
Value Name Reference
5 B-SFRR-Ready Association Section 3.1
6 B-SFRR-Active Association Section 3.2

7. References

7.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC2205]
Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, DOI 10.17487/RFC2205, , <https://www.rfc-editor.org/info/rfc2205>.
[RFC2747]
Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic Authentication", RFC 2747, DOI 10.17487/RFC2747, , <https://www.rfc-editor.org/info/rfc2747>.
[RFC2961]
Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F., and S. Molendini, "RSVP Refresh Overhead Reduction Extensions", RFC 2961, DOI 10.17487/RFC2961, , <https://www.rfc-editor.org/info/rfc2961>.
[RFC3209]
Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, , <https://www.rfc-editor.org/info/rfc3209>.
[RFC4090]
Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, DOI 10.17487/RFC4090, , <https://www.rfc-editor.org/info/rfc4090>.
[RFC4872]
Lang, J.P., Ed., Rekhter, Y., Ed., and D. Papadimitriou, Ed., "RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery", RFC 4872, DOI 10.17487/RFC4872, , <https://www.rfc-editor.org/info/rfc4872>.
[RFC6780]
Berger, L., Le Faucheur, F., and A. Narayanan, "RSVP ASSOCIATION Object Extensions", RFC 6780, DOI 10.17487/RFC6780, , <https://www.rfc-editor.org/info/rfc6780>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.

7.2. Informative References

[RFC5920]
Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", RFC 5920, DOI 10.17487/RFC5920, , <https://www.rfc-editor.org/info/rfc5920>.

Acknowledgments

The authors would like to thank Alexander Okonnikov, Loa Andersson, Lou Berger, Eric Osborne, Gregory Mirsky, and Mach Chen for reviewing and providing valuable comments on this document.

Contributors

Nicholas Tan
Arista Networks

Authors' Addresses

Mike Taillon
Cisco Systems, Inc.
Tarek Saad (editor)
Juniper Networks
Rakesh Gandhi
Cisco Systems, Inc.
Abhishek Deshmukh
Juniper Networks
Markus Jork
128 Technology
Vishnu Pavan Beeram
Juniper Networks
RFC 8796: RSVP-TE Summary Fast Reroute Extensions for Label Switched Path (LSP) Tunnels
Proposed Standard